log.Fatal() を使用して Go 関数を効果的にテストするにはどうすればよいですか?

package main

import (
    "log"
)

func hello() {
    log.Print("Hello!")
}

func goodbye() {
    log.Fatal("Goodbye!")
}

func init() {
    log.SetFlags(0)
}

func main() {
    hello()
    goodbye()
}

package main

import (
    "bytes"
    "log"
    "testing"
)

type BufferLogger struct {
    buf bytes.Buffer
}

func (l *BufferLogger) Println(v ...interface{}) {
    l.buf.WriteString(fmt.Sprintln(v...))
}

func TestHello(t *testing.T) {
    l := &BufferLogger{}
    log.SetOutput(l)

    hello()

    wantMsg := "Hello!\n"
    msg := l.buf.String()
    if msg != wantMsg {
        t.Errorf("%#v, wanted %#v", msg, wantMsg)
    }
}

func (l *BufferLogger) Fatalf(format string, v ...interface{}) {
    l.buf.WriteString(fmt.Sprintf(format, v...))
}

func TestGoodbye(t *testing.T) {
    l := &BufferLogger{}
    log.SetOutput(l)

    goodbye()

    wantMsg := "Goodbye!\n"
    msg := l.buf.String()
    if msg != wantMsg {
        t.Errorf("%#v, wanted %#v", msg, wantMsg)
    }
}